Compression-ignition engines are typically equipped with a glowplug system. The glowplug system provides a general combustion aid during engine ignition and also during a warm-up phase of the running engine. A key component of this system is the glowplug whose tip can rise up to high temperatures of above 900° C. by means of an electrical to thermal power conversion.
Each cylinder is equipped with one glowplug which is turned on when needed on the base of engine and environmental conditions, typically in cold conditions. Glowplugs function as electrical resistors. Their resistance varies with temperature. As the temperature increases, the internal resistance increases, too.
Different technologies for glowplugs are in use. Glowplugs may be high or low voltage and they may be of different materials, such as metallic or ceramic glowplugs. High voltage glowplugs are typically supplied directly by a vehicle battery. Low voltage glowplugs in contrast, as they have a nominal voltage lower than the battery voltage, typically need a pulse width modulation (PWM) supply to get the correct voltage. Especially the low voltage glowplugs can be controlled easily by connecting the gates of MOSFETS of the PWM to an electronic control unit and controlling the duty cycle of the PWM.